Pine Research MSR 636A, User Manual, Page: 133 / 176

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DRU10002 (REV 004 / JAN 2017)
mimic flow-induced pipeline corrosion conditions in the laboratory. Development
of the RDE and RRDE as routine analytical tools has largely been carried out by
the community of academic electroanalytical chemists, while the RCE has
primarily been a tool used by the corrosion and electroplating industries.
10.2 Half Reactions
Regardless of the rotating electrode geometry being used, the common theme
is that an ion or molecule is being conveyed to the electrode surface, and upon
arrival, it is either oxidized or reduced depending upon the potential applied to
the rotating electrode. If a sufficiently positive potential is applied to the
electrode, then the molecules (or ions) tend to be oxidized, and conversely, if a
sufficiently negative potential is applied to the rotating electrode, the molecules
(or ions) tend to be reduced.
Reduction at a rotating electrode implies that electrons are being added to the
ion or molecule by flowing out of the electrode and into the solution. A current
travelling in this direction is said to be a cathodic current. The general form of a
reduction half-reaction occurring at an electrode may be written as follows:
O + n e
–
→ R
where
R
represents the reduced form of the molecule (or ion),
O
represents the
oxidized form of the molecule (or ion), and
n
is the total number of electrons
added to the molecule (or ion) when it is converted from the oxidized form (
O
) to
the reduced form (
R
).
Oxidation at a rotating electrode implies that electrons are being removed from
an ion or molecule and are travelling out of the solution and into the electrode.
A current travelling in this direction is said to be an anodic current, and the
oxidation occurring at the electrode can be represented by the following redox
half reaction,
R → O + n e
–
Given that electrochemical half reactions can occur in either direction, they are
often written using chemical equilibrium notation* as follows:
O + n e
–
⇌
R
* By convention, redox half reactions are generally tabulated in textbooks and other reference
works as reduction reactions (with the oxidized form on the left side and the reduced form on
the right side, as shown above), but it is understood that the reaction may occur in either
direction depending upon the potential applied to the electrode.